This invention relates to metal musical instrument strings, such as guitar, bass and piano strings, and more particularly to shortening the break-in period while at the same time extending the useful (prime sound) period.
Metal strings for musical instruments are either a single strand of wire or a core of nylon or silk tightly wrapped helically with a strand of wire, or a wire that is itself tightly wrapped helically with a strand of wire. Thus, the core of a wound string may itself be a strand of wire. The wound string will generally follow the basic laws of physics pertaining to a vibrating string under tension. Both the wound string and the single strand string require a break-in period, and their useful period is limited due to corrosion and the continuing process of "wearing-in."
The "break-in" period is characterized by "partials," which are tones disproportionate (in both amplitude and frequency) to the harmonics expected of the string. These partials can be described as extra brilliant to harsh, with the harshness quality generally attributed to many unpredictable partials. Another characteristic of the break-in period is the instability of the string to maintain tune. This instability manifests itself in a drifting of the frequency to which it is tuned.
The mechanism of the break-in period for the wound string is easier to visualize. When the string is in tension and played (displaced), the windings change position relative to each other, and relative to the core, and as the string returns to its rest position, the windings tend to return to their original position. Under vibration, there is continuous change of position. Due to surface roughness of the windings and the core, particularly if it is metal, there is not a smooth change of position as the string changes from an extreme of displacement on one side through the rest position to displacement on the other side. It is this roughness that produces the partials.
It is easy to observe this roughness through a 40.times. microscope in a string that has a 0.011" diameter core, a winding of 0.004" diameter wire for a total string diameter of 0.019". A string that has a core diameter of 0.020" and a winding of wire having a diameter of 0.017" (for a total string diameter of 0.054") will show its roughness even more easily. A single strand of wire will also show such roughness, and cause the same partials and instability observed with the wound strings for essentially the same reason. If viewed in a microscope with magnification much greater than 40.times., the surface will appear like shattered safety glass with cracks running at random in every direction. Adjacent pieces of the cracked surface rub against each other as the string is played so that, until worn smooth during the break-in period, partials and instability will be experienced.
Once the string is broken-in, there is a continuous process of corrosion, which causes roughness, and wearing smooth the roughness due to corrosion. Consequently, an instrument that is played frequently will stay in tune and yield the expected harmonics, but with a limited useful life. An instrument played only infrequently will require retuning followed by another break-in period. In either case, there is continuous corrosion due to the atmosphere, as well as the acids and salts on the fingers of the person playing the instrument. It is this process of continuous corrosion and wearing smooth that limits the useful life (prime period) of the string, after which the string enters a "dead period" characterized by the string having a dull tone (very limited harmonics and very little sustain). It also does not stay in tune at all positions along the string.